1
 Epidemiology
2
Classically speaking

• Epi upon (among)
• Demos people
• Ology science
• Epidemiology the science which deals with what
  falls upon people..

3
A Modern Definition

• The study of the distribution and determinants
  of health-related states in specified
  populations, and the application of this study to
  control health problems."
• (Last J)

Search for knowledge Apply in health
service
4
Objectives of Epidemiology

• 1. To describe the distribution and magnitude of
  health and disease problems in the population.
• 2. To identify the etiological factors risk
  factors in the population.
• 3. To provide the data essential to planning,
  implementation and evaluation of services for
  prevention, control and treatment of disease and
  to setting up of priorities for these services.

5

• The ultimate aim of epidemiology is
• to eliminate or reduce health problem or its
  consequences
• and
• to promote health and well-being of society as a
  whole.

6
Purposes of Epidemiology

• To investigate nature / extent of health-related
  phenomena in the community / identify priorities
• To study natural history and prognosis of
  health-related problems
• To identify causes and risk factors
• To recommend / assist in application of /
  evaluate best interventions (preventive and
  therapeutic measures)
• To provide foundation for public policy

7
Component

• Disease Frequency- Rate and Ratio e.g
• Rate- incidence rate,
  prevalence rate etc
• Ratio- sex ratio, doctor-population ratio
• Distribution of Disease-
• Disease in community find causative
  factor
• Generate hypothesis
• Descriptive epidimiology

8

• Determinants of Disease-
• To test hypothesis
  
• Analytic epidemiology
  
• Help in
  develop sound scientific
  program

9
Incidence

• Number of new cases of a disease which come into
  being during a specified period of time.
• (Number of new cases of specific disease
  during a given period)/(population at risk during
  that period) x 1000
• Importance If incidence increasing, it may
  indicate failure or ineffectiveness of control
  measure of a disease and need for better/new
  health control measure.

10
Prevalence

• Number of current case (old and new) of a
  specified disease at a point of time
• It help to estimate the burden of disease
• Identify potentially high-risk populations. They
  are essentially helpful to plan rehabilitation
  facilities, manpower needs, etc.
• (Number of current case of a specified disease
  at a point of time)/(estimated population at the
  same point of time) x 100
• Point prevalence AND Period prevalence

11
Relationship between incidence and prevalence

• Prevalence Incidence x Duration

12
Approach of an epidemiologist

• Asking questions
• making comparisons
• ? Asking questions may provide clues to cause or
  aetiology of disease e.g.
• What is the event,
• what is its magnitude,
• where did it happen,
• when did it happen,
• who were affected,
• why did it happen?

13

• Making comparisons will help draw inferences to
  support asking questions.
• This comparison may be
• ? Between those with the disease and those
  without the disease
• ? Those with risk factor and those not exposed to
  risk factor

14
Terms to know

• Endemic constant presence of a disease in a
  given population
• epidemic outbreak or occurrence of one specific
  disease from a single source, in a group
  population, community, or geographical area, in
  excess of the usual level of expectancy
• pandemic epidemic that is widespread across a
  country, or large population, possible worldwide

15
Three essential characteristics that are examined
to study the cause(s) for disease in analytic
epidemiology are...

• Host
• Agent
• Environment

16
(No Transcript)
17
Host Factors

• Behaviors
• Genetic predisposition
• Immunologic factors

• Influence the chance for disease or its severity

18
Agents

• Biological
• Physical
• Chemical

• Necessary for disease to occur

19
Environment

• External conditions

• Contribute to the disease process

20
Epidemics arise when host, agent, and
environmental factors are not in balance

• Due to new agent
• Due to change in existing agent (infectivity,
  pathogenicity, virulence)
• Due to change in number of susceptibles in the
  population
• Due to environmental changes that affect
  transmission of the agent or growth of the agent

21
EPIDEMIOLOGICAL METHODS

• .
• The methods he employs can be classified as
• 1. Observational studies
• a. Descriptive studies
• b. Analytical studies
• Case control studies
• Cohort studies
• 2. Experimental/interventional studies
• Randomized control studies
• Field trials
• Community trials

22

• Descriptive Studies
• Steps in conducting a descriptive study.
• Descriptive studies form the first step in
  any process of investigation.
• These studies are concerned with observing
  the distribution of disease in populations.
• 1. Defining the population.
• 2. Defining disease under study.
• 3. Describing the disease.
• 4. Measurement of disease
• 5. Compare
• 6. Formulate hypothesis-

23

• Defining the population. Defined population may
  be the whole population or a representative
  sample.
• It can also be specially selected group such as
  age and sex groups, occupational groups, hospital
  patients, school children, small community, etc.

24

• 2. Defining disease under study.
• 3. Describing the disease.
• Disease is examined by the epidemiologist by
  asking three questions
• ? When is the disease occurringtime
  distribution?
• ? Where is it occurringplace distribution?
• ? Who is getting the diseaseperson distribution?

25

• A. Time Distribution
• Short-term fluctuations.
• Epidemic
• Common source epidemics
• - single exposure/point sourcebhopal
  tragedy
• Propagated-infectious
• -
• Periodic fluctuations
• Seasonal measles (early spring)
• cyclic- ,, in pre-vaccinated
  era (peak 2-3 yr)
• Long-term or secular trends diabetes, CVD

26

• B. Place Distribution
• International variations
• Cancer of stomach very common in Japan
• less common in US.
• oral cancer- India
• Breast cancer- Low-japan, high-western
• National variations, e.g. Distribution of
  fluorosis,

27

• Rural-urban differences, e.g.
• CVD, Mental illness more common in urban areas.
• Skin diseases, worm infestations more common in
  rural areas.
• Local distributions, e.g. Spot maps- John Snow in
  London to incriminate water supply as cause of
  cholera transmission in London.

28
cholera cases in proximity to water pump, 1854
29
(No Transcript)
30

• C. Person Distribution
• Age e.g.
• Measles is common in children,
• Cancer in middle age
• Degenerative diseases in old age.
• Sex
• Women- Lung cancer-less
• Hyperthyroidism- more
• c. Social class- Diabetes, Hypertenson upper
  class

31

• 4. Measurement of disease- Mortality/ Morbidity
• 5. Compare- Between different population,
  subgroups
• 6. Formulate hypothesis. On basis of all data
  epidemiologist form hypothesis.